The earth is surrounded by layers of gases, our atmosphere. They are kept near the earth’s surface by gravity.

Our atmosphere filters the sunlight and keeps dangerous rays from reaching our planet. Without such a filter it would get too hot during the daytime. At night it prevents heat from escaping so it does not get too cold.

Without an atmosphere life on our planet would not be possible. It also makes our world a more pleasant place to live. Air carries sound waves, which let us hear voices or listen to music. The atmosphere creates rainbows, makes the sky turn blue on clear days and the sun red when it sets

 

The makeup of our atmosphere
The air near the earth’s surface consists of 77 percent nitrogen and about 21 percent oxygen. Carbon dioxide is also present, but only in small amounts. Nevertheless it is very important because green plants use it when they make their food. Higher up you can find helium and hydrogen in the atmosphere.

Not all gases are created by nature, some are produced by people. Methane rises into the atmosphere from decaying plants and animals. Carbon monoxide and chlorofluorocarbons (CFCs) enter the atmosphere because of industrial activities.

 

Weight and Pressure
We often think that the air is weightless but it isn’t. The whole weight of the earth’s atmosphere is about 5.5 quadrillion tons (55 followed by 14 zeros). Air is heaviest at sea level because the air molecules are pressed together. It also presses against our bodies but we have pressure inside , so we don’t feel it. When you move farther away from the earth’s surface the atmosphere gets lighter and lighter because there is more room between air molecules. The weight of the air decreases and so does air pressure.